Performance oriented boaters typically wish to obtain the greatest power output possible. However, the output produced by most boat engines is limited by the stern drive unit. This unit transmits the power from the boat's motor to the propeller shaft. It houses the vessel's clutch and U-joint assemblies, as well as various gears and bearings. These components undergo tremendous stresses and strains as the engine is operated. Accordingly, a standard oil reservoir is used to lubricate the drive components and minimize wear. Nonetheless, over time and particularly under heavy use, the oil deteriorates. Eventually, the internal components of the stern drive, such as the top bearing, become misaligned and fatigued. No matter how carefully it is maintained, the stern drive will fail at some point. High performance boat engines are particularly susceptible to premature stern drive problems because of the extreme heat generated in the drive. Indeed, in many high performance engines, the oil temperature approaches 290 degrees Fahrenheit.
To date, the stern drive has been cooled by allowing it to be sprayed by the surrounding (ambient) water. This technique has generally not proven to be satisfactory. Stern drives, and particularly those used in high performance watercraft, still exhibit an undesirably high and premature rate of failure. Frequent and costly stern drive repairs are a relatively commonplace problem.